The present invention provides a method for preparing an encapsulated cathode material, and more particularly, to a method for encapsulating an insertion compound within an ionically and electronically conducting polymeric wall.
Solid state lithium electrochemical cells are known in the art. Typically they consist of a lithium or lithium-based foil anode, a lithium ion conducting polymeric electrolyte, and a cathode based on an insertion electrode material such as V.sub.6 O.sub.13. In order to achieve high active cathode utilization, the cathode has been constructed as a composite comprising the electrode material, a polymeric electrolyte, and an electronically conducting medium such as graphite. Previously, as described in U.S. Pat. No. 4,589,197 to North, these composites have been prepared from a solution of the cathode components in a solvent such as acetonitrile. The solution is cast onto a current collector and the solvent is evaporated to give a sheet or film of the composite cathode on the current collector. In accordance with the teachings of North, the composite cathode is additionally subjected to densification by pressure rolling.
U.S. Pat. No. 4,576,883 to Hope teaches a cathode construction having increased surface area, increased performance characteristics and increased active life in which the insertion compound is encapsulated in an electronically and ionically conducting polymeric material. The principal advantage of encapsulating the insertion compound in the polymeric sphere is a large increase in the available active surface area of the cathode. The insertion compound is also mechanically fixed which increases the active life of the cathode layer.